Disc drives are used to store digitally encoded information. Digital information is stored on rigid discs supported for rotation for read and write operations. Heads including transducer elements are supported relative to the disc surface to read data from and write data to the disc surface. An E-block movably supports heads relative to the disc surface to read data from concentric data tracks on the disc. A voice coil motor moves E-block to position heads relative to selected data tracks on the disc surface.
The movement of the head to a desired data track is referred to as seeking. Maintaining the head over the center of the desired data track during read and write operations is referred to as track "following". Operation of the E-block (and heads) is controlled by a servo control system using prerecorded servo information or position feedback either on a dedicated servo disc or on sectors interspersed among the data on a data disc. Loss of position feedback interferes with servo control and can cause the E-block and head to contact or slam into an end stop. Rapid movement or acceleration of the E-block into the end stop can damage heads and degrade air bearing stiffness.
In prior servo control systems, the E-block is slowed when there is a loss of position feedback to reduce the force at which the E-block slams into the end stop. To slow the E-block, the voltage potential across the voice coil motor is electrically shorted and the back Electro-motive force (Emf) is used to supply a brake current to slow the E-block. Although, the back Emf slows the E-block to reduce the force at which the E-block contacts the end stop, the lag time for the back Emf to stop the E-block can be relatively long in comparison to the operating stroke of the E-block. A relatively long lag time increases the stopping time and force at which the E-block contacts the end stop. The present invention addresses these and other problems, and offers other advantages over the prior art.